The present invention relates to an image-forming lens unit for use in an image reading apparatus for example. The present invention also relates to an image reading apparatus incorporating such a lens unit.
Conventionally, various types of image reading apparatus are used for reading an image carried on a document. For example, there exists an image reading apparatus which reads an image of a document line by line (each line extending in the primary scanning direction). This type of image reading apparatus includes a plurality of light receiving elements arranged in a row. Accordingly, for forming an image of a document on these light receiving elements, a lens unit (lens array) need be used which includes a plurality of lenses arranged in a row extending in the primary scanning direction.
FIG. 42 illustrates an example of prior art image reading apparatus. The image reading apparatus includes a case 100 having a hollow portion, and a transparent plate 101 fitted in an upper portion of the case. The transparent plate 101 contacts a document D which is pressed against the plate by a platen roller 102. By the rotation of the platen roller 102, the document D is transferred in a direction indicated by an arrow Td (which is perpendicular to the primary scanning direction). The transparent plate 101 has an upper surface which includes a linear image read area Sa extending in the primary scanning direction. For irradiating the image read area Sa with light, a light source 103 is provided in the case 100. A lens array 104 is provided below the image reading area Sa. The lens array 104 includes a plurality of lenses 105 arranged in a row extending in the primary scanning direction. As shown in FIG. 42, light from the image read area Sa is collected by the lenses 105 to be received by a plurality of light receiving elements 106 provided thereunder. Similarly to the lenses 105, the plurality of light receiving elements 106 are arranged in a row extending in the primary scanning direction.
FIG. 43 is a perspective view showing the entirety of the lens array 104. As shown in this figure, the plurality of lenses 105 are held by an elongated holder portion 104a. 
Each lens 105 is a columnar self focusing lens (selfoc lens) the refractive index of which varies depending on the distance from the central axis. Therefore, as shown in FIG. 44, light traveling within the lens 105 follows a tortuously bent path. By using such a lens, an object a-b and its image axe2x80x2-bxe2x80x2 become equal in orientation and size.
In a prior art method for making the lens array 104, prior to the formation of the holder 104a, lenses 105 are formed. Thereafter, the holder 104a are so formed by resin molding (insert molding) as to embed the lenses 105. Thus, in the prior art method, the formation of the plurality of lenses 105 and the molding of the holder 104 are performed in separate process steps. This method is disadvantageous because the lens array 104 cannot be made efficiently.
The above-described problem becomes more serious due to the fact that a large number of lenses 105 are necessary for making a lens array 104 and that each lens 105 is very small. That is, each lens 105 needs to be precisely positioned relative to the holder 104a. For the lens array 104 which deals with a large number of small lenses, it is clearly very difficult to perform such positioning precisely and efficiently.
The image reading apparatus as shown in FIG. 42 also has the following problems.
For reading an image at a high resolution, a document image need be formed by the lenses 105 without blurring. For this purpose, it is necessary to precisely set a distance La between the upper surface 105a of each lens 105 and the document G to a predetermined value. However, in an actual image reading process, the document G may rise from the transparent plate 101 so that the distance La may become longer than the predetermined length. Such a problem occurs more often in a hand-held scanner type image reading apparatus which does not include a platen roller.
In the prior art apparatus, therefore, the focal depth of each lens 105 is set large so that the image reading can be performed at a high resolution even when the distance La becomes slightly longer than the focal distance.
However, for making the focal depth of the lenses 105 large, the distance La need be set long. Further, when the focal depth is made large, the focal distance of each lens 105 becomes longer, so that a distance Lb (the distance between the lower surface 105b of each lens 105 and each light receiving element 106) need be made longer. As a result, in the prior art image reading apparatus, the distance between the transparent plate 101 and the light receiving elements 94 becomes long, which increases the size of the image reading apparatus.
An object of the present invention is to provide a lens unit which is capable of eliminating or at least lessening the above-described problems.
Another object of the present invention is to provide an image reading apparatus utilizing such a lens unit. A lens array which is provided in accordance with a first aspect of the present invention comprises: a body including a plurality of lenses and a holder portion for holding the lenses; and separating means for optically separating the plurality of lenses from each other; wherein the plurality of lenses and the holder portion are formed of a light-permeable resin and integral with each other.
In a preferred embodiment, the body includes an upper surface, and a lower surface opposite to the upper surface, and at least one of the upper and the lower surfaces is provided with a plurality of projections or recesses corresponding to the plurality of lenses.
Preferably, the separating means includes light-shielding portions for absorbing light.
In a preferred embodiment, the body includes a plurality of hollows provided adjacent to the plurality of lenses. The light-shielding portions include a dark-colored coating applied to wall surfaces of the body which define the hollows. Herein, the dark color may preferably be black. However, the present invention is not limited thereto, and any other color may be applicable if only it blocks or absorbs light.
Instead of the dark-colored coating, the light-shielding portions may be formed by inserting dark-colored members into the hollows.
In a preferred embodiment, the hollows are so provided as not to penetrate through the body.
In another preferred embodiment, the hollows are so provided as to penetrate through the body.
The hollows may be arranged in a row. In this case, each of the hollows may extend linearly in a direction intersecting the row.
The plurality of hollows may be generally cylindrical for surrounding the plurality of lenses, respectively.
The plurality of hollows may be so formed as to make the plurality of lenses tapered.
In a preferred embodiment, the light-shielding portions include dark-colored members embedded in the body.
In a preferred embodiment, the light-shielding portions include portions of the body which are dark-colored.
Preferably, the lens array of the present invention further includes a light-shielding member for covering an outer surface of the holder portion.
In a preferred embodiment, the plurality of lenses are arranged in a matrix, and the body is in the form of a plate.
In accordance with a second aspect of the present invention, there is provided a lens array comprising: a plurality of lenses; and a holder portion for holding the plurality of lenses; the lens array further including a plurality of hollows located adjacent the plurality of lenses; wherein the plurality of lenses and the holder portion are formed of a light-permeable synthetic resin and integral with each other.
In accordance with a third aspect of the present invention, there is provided a lens unit comprising: a first lens array including a plurality of first lenses, a first holder portion for holding the first lenses, and first separating means for optically separating the first lenses from each other; and a second lens array including a plurality of second lenses, a second holder portion for holding the second lenses, and second separating means for optically separating the second lenses from each other. The first lenses and the first holder portion are formed of a light-permeable resin and integral with each other, and the second lenses and the second holder portion are formed of a light-permeable resin and integral with each other. The first lens array and the second lens array are laminated on each other so that each of the first lenses and a corresponding one of the second lenses are aligned on a common optical axis.
Preferably, the first and the second lens arrays are provided with positioning means for positioning the first and the second lens arrays relative to each other.
The first and the second lenses may be spherical lenses. Some of the first and the second lenses may be aspherical lenses.
In a preferred embodiment, the lens unit of the present invention further comprises a third lens array including a plurality of third lenses, a third holder portion for holding the third lenses, and third separating means for optically separating the third lenses from each other.
Preferably, the first and the second lenses are convex lenses and the third lenses are concave lenses. The third lenses are different in Abbe number from the first and the second lenses.
In accordance with a fourth aspect of the present invention, there is provided a lens unit comprising: at least one lens array including a plurality of lenses each of which has a first surface and a second surface; a housing for accommodating the lens array; a first opening provided in the housing at a position which is closer to the first surface than to the second surface; a second opening provided in the housing at a position which is closer to the second surface than to the first surface; a first light guide means for guiding light traveling through the first opening into the housing toward the second surface of the lens; and a second light guide means for guiding light emitted from the first surface of the lens toward the second opening.
In accordance with a fifth aspect of the present invention, there is provided a method of making a lens array. This method comprises: a first step of forming a plurality of lenses and a holder portion for holding the lenses by molding a light permeable resin; and a second step of providing separating means for optically separating the plurality of lenses from each other; wherein the plurality of lenses and the holder portion are integrally formed with each other in the first step.
In a preferred embodiment, a plurality of hollows are formed adjacent to the plurality of lenses in the first step, and dark-colored light-shielding members are provided in the plurality of hollows in the second step.
Preferably, in the first step, a plurality of lens arrays are collectively formed by resin molding using a mold having a plurality of cavities.
In a preferred embodiment, in the second step, a jig to which a dark-colored coating is applied is inserted in the hollows to transfer the coating onto wall surfaces defining the hollows.
Preferably, the method of making a lens array according to the present invention further comprises the step of applying a black coating to an outer surface of the holder portion after masking a light entering surface and a light emitting surface of each of the plurality of lenses.
In accordance with a sixth aspect of the present invention, there is provided an image reading apparatus comprising: a lens unit including a plurality of lenses for collecting light traveling from a linear image read area, each of the lenses having a first surface, and a second surface which is located farther from the image read area than the first surface; and a plurality of light receiving elements for receiving the collected light; wherein the image reading apparatus further includes a first light guide means for guiding light traveling from the image read area toward the second surface of said each lens, and a second light guide means for guiding light emitted from the first surface of said each lens toward the plurality of light receiving elements.
Preferably, the light traveling from the image read area passes one side of said each lens and then changes its traveling direction by the first light guide means to reach the second surface of the lens. Further, the light emitted from the first surface of the lens changes its traveling direction by the second light guide means to pass the other side of the lens to be received by the plurality of light receiving elements.
The first and the second light guide means may comprise a prism. Alternatively, the first and the second light guide means may comprise a plurality of mirrors.
In a preferred embodiment, the lens unit includes a first lens array and a housing for fixing the first lens array. The first lens array, the first light guide means, and the second light guide means are incorporated in the housing.
Preferably, the housing is dark-colored, and the plurality of light receiving elements are covered with the housing.
Preferably, the image reading apparatus according to the present invention further includes a light source for illuminating the image read area, a case for accommodating the light source and the plurality of light receiving elements. The first lens array, the first light guide means and the second light guide means are directly attached to the case.
Preferably, the lens unit includes a second lens array including a plurality of lenses, and the first and the second lens arrays are laminated on each other so that each lens of the first lens array and a corresponding one of the second lens array are aligned on a common optical axis.
Each of the plurality of lenses may comprise either a selfoc lens or a lens formed of optical fibers.
Other features and advantages of the present invention will become clearer from the detailed description given below with reference to the accompanying drawings.